基于竖向循环荷载下锚杆长度对锚杆锚固机理的数值模拟分析

Numerical Simulation Analysis of Anchor Mechanism based on Anchor Length under Vertical Cyclic Load

为了揭示在循环荷载作用下全长粘结性锚杆的锚固机理,使用有限差分程序FLAC3D建立锚杆拉拔模型,研究循环荷载作用下锚杆各个位置的轴力、位移、锚-土界面剪应力和土体位移速率、锚杆顶端位移、循环荷载位移比随循环荷载幅值比的变化规律。主要研究结论如下:1)在静载作用下,锚杆端头位移随着荷载的增大而增大;当竖向拉拔荷载超过极限拉拔力时,锚杆顶端位移不收敛;当竖向荷载增大时,不同长度锚杆模型的界面剪应力也随之增大,直至剪应力增加到最大值后平衡,此时锚-土界面发生破坏;锚固孔径不变,锚杆长度变化并不影响锚-土界面剪应力峰值。2)通过施加循环荷载,增大循环荷载的加载周期与幅值,锚杆顶端位移随之增加;不同长度的锚杆顶端位移与循环次数呈线性变化;锚-土界面剪应力跟随循环荷载的幅值增大而增大,呈先增大后减小的趋势;在一个周期循环下,施加循环荷载的锚杆位移明显大于静载作用下的锚杆位移,并且通过拟合曲线发现循环荷载比随着循环位移比呈线性变化。3)对锚杆锚固机理进行敏感性分析,敏感性大小依次是循环荷载比、锚杆长度、周期。

In order to reveal the anchoring mechanism of full-length cohesive anchor under cyclic load,the finite difference program FLAC3D is used to establish the anchor pull-out model to study the axial force,displacement,shear stress at the anchor soil interface,soil displacement rate,displacement at the top of the anchor and the variation of cyclic load displacement ratio with cyclic load amplitude ratio at various positions of the anchor under cyclic load.The main conclusions are as follows.Firstly,under the static load,the displacement of the anchor rod tip increases with the increase of the load;When the vertical pull-out load exceeds the ultimate pull-out force,the displacement of the top of the anchor rod does not converge;When the vertical load increases,the interface shear stress of different length anchor models also increases until the shear stress increases to the maximum value,and then the anchor soil interface is destroyed;The change of anchor length does not affect the peak shear stress of anchor soil interface.Secondly,by applying the cyclic load,the loading period and amplitude of the cyclic load are increased,and the displacement of the top of the anchor rod is increased;The displacement of the top of the anchor rod with different length varies linearly with the number of cycles;The shear stress of the anchor soil interface increases with the increase of the cyclic load amplitude,which increases first and then decreases;In one cycle,the displacement of the anchor rod under cyclic load is significantly greater than that under static load.Through fitting curve,it is found that the cyclic load ratio changes linearly with the cyclic displacement ratio.Thirdly,the sensitivity of anchor mechanism is analyzed,and the sensitivity is cyclic load ratio,anchor length and period in successive order.